1. Field of the Invention
The present invention relates to an ISDN (Integrated Services Digital Network) interface unit mounted on a data processing unit e.g., a personal computer or the like, for processing an interface between an ISDN line and the data processing unit, and particularly to an ISDN interface unit using a higher grade service that can be provided without depending on a communication partner's ISDN progress, or communication speed, and also relates to an ISDN interface unit using a connected analog telephone that can ring.
2. Description of the Related Art
It is advantageous for a communication terminal to execute a multi-media communication service to which an ISDN high speed communication or a plurality of channel functions is applied, using an existing personal computer. In this regard, although the ISDN can provide a high grade communication service, since the connecting sequence is complicated compared with a conventional telephone network, the interface circuit connecting between the personal computer and the ISDN is necessary. As an interface circuit, there is a terminal adaptor and an ISDN interface unit. The terminal adaptor is provided with a module corresponding to a modem in a conventional analog line, it is connected to an RS232C port (American National Standards Institute) in the personal computer or the like, and a data communication through the ISDN is realized. On the other hand or alternatively, the ISDN interface unit maybe mounted is an option slot in the personal computer, and a physical connection to the ISDN or a connecting sequence to the ISDN exchange is realized.
The purpose of the conventional ISDN interface unit is to form a combination of the information processing of the personal computer and the digital information communication, and generally it has both the ISDN connecting function and the data communication function e.g., data link control function or the like. Further, by controlling the connecting sequence from the personal computer, it is constituted or constructed such that a higher grade telephone service can be realized. By providing an audio apparatus for the telephone (e.g., handset or the like) service hereinafter, some of the conventional ISDN interface units are constituted to provide a voice communication service.
In the conventional ISDN interface unit, however, as a first problem, the data communication service and the voice communication service are treated independently, and storage into the personal computer of the digital voice signal from the line and the transmission of the voice data in the personal computer to the line, cannot be carried out. Accordingly, in the conventional ISDN interface unit, for example, storage of the digital voice signal in the personal computer, the playback of the stored digital voice signal by the PCM (Pulse Code Modulation) sound source, and reuse of the voice data, cannot be executed, because of the different coding between the voice data by the PCM sound used in the personal computer and the voice data used in the ISDN line.
In addition, as a second problem, in the conventional ISDN interface unit, only digital communication is realized and data communication in the voice band signal is not supported. For example, in the terminal adaptor, the conversion from the digital signal (e.g., speed of 9600 bps) of the standard of the RS232C to the digital signal series of the ISDN 64 kbps is realized. The conversion realizes the V.110 standard standardized by CCITT. Some of the conventional ISDN interface units are provided with the above rate adaptation function. In the conventional ISDN interface unit, however, in this case, the conversion to the voice band signal realized by the modem cannot be executed. Namely, only digital data communication is realized, and data communication in the voice band signal is not supported. Therefore, by using the conventional ISDN interface unit, communication to the network information service center or the like connected to the existing analog network cannot be carried out.
Further, as another problem in the conventional example, in order to produce the ring of an analog telephone, a high voltage and low frequency signal of 75 Vrms and 16Hz is necessary. In the conventional telephone network, the ring is generated in the telephone exchange station.
When the analog telephone is connected to the ISDN, which does not generate a ring, hitherto, there arises a problem in that the analog telephone cannot produce the ring.
As one method for the above problem, it is considered that the ISDN interface unit connected to the analog telephone, and processing the interface process to the ISDN, provides a ring signal generator generating a ring signal. However, the ring signal generator generating a ring signal having a high voltage and low frequency, such as 75 Vrms and 16 Hz, must be very large. On the other hand, the above-mentioned ISDN interface unit requires a small size to realize the various functions, for example, the extended board in the personal computer. Accordingly, in fact, the above scale cannot be used.